9 Common Lawn Diseases Every Homeowner Needs to Know – and the Best Ways to Treat Them
Identifying lawn diseases is the first step in stopping them. Here are the most common ones you'll come across and how to get rid of them.
A glorious green grass is a prominent feature of the home, but lawn diseases can ruin that picture-perfect expanse of emerald. Common grass diseases often cause bald patches, discolored blades, rings, and other anomalies.
Lawn disease control should start in early spring just before new growth emerges with a second application in fall that will further protect your turfgrass. Lawn diseases may be viral, bacterial, or fungal, although viral disease is rare in turfgrass. These problems can stem from improper lawn care, environmental conditions, or different pathogens. There are specific treatments for each, but the first step is identifying which issue is impacting your lawn.
I’ll walk you through the most common lawn diseases that plague home landscapes. Then I’ll share my top tips on how to prevent and treat these problems.
Common Lawn Diseases
Sometimes improper lawn care is responsible for unsightly lawns, but often it is caused by a large number of pathogens. Recognizing the disease is key to lawn disease control.
Lawn disease treatment is relatively specific to the type of pathogen, like using different fungicides for different fungal lawn diseases. Similarly, bactericides work on most but not all bacterial diseases.
Here are the most common lawn diseases and how to identify which one is impacting your yard.
1. Brown Patch
Brown patch may resemble the damage done by dogs, but the irregular, rounded dead patch is composed of blades with tan lesions that have darker edges. Over time, the rounded patches can extend out into larger areas.
In the morning dew, you can observe spider web-like purple to gray growth over the blades of grass. This is the fungus that is causing the disease. It is most prevalent in humid weather on cool-season grasses. The development of the fungus can almost fully encompass the lawn site if left untreated.
2. Dollar Spot
Dollar spot appears as small, rounded patches of bleached grass. They are the size of a silver dollar, which leads to the common name of this disease. As the disease progresses, the spots begin to blend together.
This disease is also caused by a fungus, which shows in the early morning as silver-white threads atop the grass blades. The fungus favors warm, humid conditions and is easily spread by walking on your lawn or with mechanical equipment. Large areas of the grass can die when left untreated.
3. Fairy Ring
Although the name is rather cute, a fairy ring is a severe disease that results in uneven areas that are bordered by darker green. When conditions are very wet, mushrooms can also appear in the darker green border.
The disease symptoms show in early spring when cool, damp weather fuels fungi. The fungus begins at a central point and radiates outward, leaving weak grass at the center that can become susceptible to other diseases.
4. Melting Out
Melting out is a disease that occurs when the weather is wet and cool. It can cause very large patches of yellow grass with sparse blade growth and loose plant material. If you take a rake to the thatch buildup that sometimes causes this disease, large clumps will easily come out. Although cool-season grasses are most often affected, it can also occur in warm-season grass varieties.
5. Leaf Spot
Several viruses and bacteria can cause leaf spot, but it can also be fungal. The blades of grass will develop small elongated brown spots with reddish or purple borders. The overall appearance of the turf may be dying out on the site. Leaf spot is most prevalent in the summer and can cause entire sections of the lawn to die out.
6. Powdery Mildew
Powdery mildew is a fungus that affects many types of plants. It is very recognizable due to the white powdery residue on the leaf blades. The fungus feeds on plant tissue and causes damage, killing the leaf over time.
In significant occurrences of powdery mildew, the leaves are stunted, the area patchy, and overall turf health is weakened. Powdery mildew prefers warm, humid conditions.
7. Red Thread
Also known as pink patch, red thread is a fungal disease that causes thread-like growth on the tips of the leaf blades in red and coral hues. It can be complicated to control and can show up overnight. The leaf blades will dwindle in numbers and the lawn will become patchy.
8. Slime Mold
As unappetizing in appearance as in name, slime mold is a moist, slick mold that covers leaf blades in a variety of colors. It can also fruit and develop tiny balls of growth on the leaves of the grass.
Slime mold is not harmful to the grass itself, but lends an unattractive appearance to the lawn. It occurs when there is too much organic matter in the soil and conditions are warm and wet.
9. Rust
Rust is a fungal disease that causes orange and brown lesions on the leaf blades. The leaves die and the resulting lawn becomes patchy and sparse. It is most common in late summer into fall when there is plentiful moisture and warmth. The fungus lives in the thatch and appears when the right conditions occur. The spores can be transported to other areas of the lawn on shoes and tools.
How to Prevent Lawn Diseases
The way you water, fertilize, and mow your lawn can affect the health of your grass beneficially or negatively. Timing of these activities is also important. Most of the common diseases of lawns are caused by fungi.
Fungi require moisture to thrive. Some prefer cool, moist locations, while others need the temperatures warmer. If you water your lawn when the grass blades cannot dry in a timely manner, fungi can take hold. Early morning is the best time to irrigate.
Too much fertilizer creates a nutrient dense environment where fungi can thrive. Sod that's grown in too much shade is prone to fungal disease and so are lawns with thick thatch. The height at which you mow can also contribute to disease. Remove just a third of the blade length each time you mow.
How to Control Lawn Diseases
- Water your lawn in the morning.
- Dethatch your lawn when the thatch is more than 0.5 inches (1.27 cm) to prevent excess moisture buildup, lack of oxygen, and nutrient density that fosters pathogens. If thatch is a common problem for you, consider a dethatcher like this one from Amazon so you can solve this issue yourself.
- Aerate your lawn if the soil is compacted to encourage water percolation, nutrient movement, air introduction, and create a healthy lawn resistant to disease. You can hire professionals to aerate or do it yourself with a home lawn aerator like this one from Amazon.
- Control weeds which can steal water and nutrients from the lawn and lead to grass that is more susceptible to disease.
- Only mow a third of the height off your grass each time to avoid damaging the sod and keep the blades tall enough to conserve moisture. This will help prevent the need for overwatering.
- Perform a soil test to determine nutrient amounts in soil for more accurate feeding of the lawn. Many soil tests can also determine soil pH, like this one from Amazon. Overly acidic soils favor many fungi while alkaline soil promotes other diseases. Aim for a pH of 6.0-7.0.
When to Bring in a Professional
If you simply don’t have the time or resources to do regular yard maintenance then it is time to call a landscaping professional. But with a maintenance regimen and schedule of tasks, most disease in the lawn is easy to prevent with the simple tips above. If your lawn is new to you or has been poorly managed for some time, bring in professionals to get the turfgrass healthy again and then take it from there.
Frequently Asked Questions
What is the most common grass disease?
The most common disease will depend upon your variety of turfgrass and where it is growing. Southern gardeners will find many different problems from Northern turf growers. Dollar spot, leaf blight, and brown spot are very common.
How do you tell if you have lawn fungus?
You may have to get on eye level with your grass to diagnose problems. Visual cues like browning or yellowing, spots in the lawn, and dieback are just some of the more common cues of fungal disease. If the leaf blade itself has spotting or necrosis, this can be another sign.
